In a conventional communication system in which a sensor transmits a detection signal to a control apparatus, the sensor and the control apparatus are configured to operate under the common time information. For example, as disclosed in US 2013/0343472 A1, the control apparatus generates a trigger signal as a request signal, and transmits the trigger signal to the sensor. In response to the request signal, the sensor transmits the sensor signal as a response signal to the control apparatus.
In the above communication system, suppose that microcomputer included in the control apparatus receives the sensor signal transmitted from the sensor at a predetermined transmission cycle, and the microcomputer calculates a time differential value of a sensor value at a predetermined calculation cycle. In this kind of communication system, when the sensor and the microcomputer operate based on different timers, a cycle shift between the transmission cycle of the sensor and the calculation cycle of the microcomputer may be occurred even though the sensor transmits the sensor signal at a constant transmission cycle and the microcomputer performs the arithmetic calculation at a constant calculation cycle. When the cycle shift occurs, the microcomputer may fail to correctly calculate the time differential value based on the sensor value.
Regarding the cycle shift, as disclosed in US 2013/0343472 A1, the microcomputer may transmit a trigger signal to the sensor, and the sensor may transmit the sensor signal in response to the reception of the trigger signal. However, in this kind of system, a delay occurred in the transmission of the trigger signal may adversely affect a calculation of the correct differential value.